why boolean modifier not making difference
Ateks,the file had several issues:


car body had no boolean(?)
car body had several unapplied modifier mirror > subsurf > edge split - those were interfering after adding a boolean modifier (it showed an error), so I applied them all
the bars HAD negative X scale(corrected)
the bars also had edge split modifier (I applied it)


in this way I could obtain this:



which should be more or less what you wished, I hope.

Here is the modified file